Durable bolted joints in steel construction 13 December 2023

The saying goes ‘everybody can tighten a bolt’, but a properly designed joint involves a multitude of factors, from preload and friction to tool calibration, settlements, as well as dynamic loads.

Nord-Lock higlights that while the requirements for welded joints have evolved steadily over the years, to the point where it’s now common to have certified professionals to execute and approve welded joints, a simple bolting protocol from anyone is sufficient for critical bolted joints. Unfortunately, even this minor requirement is not always available.

The fact that critical bolted joints are not subjected to similar quality requirements as welded joints can lead to problems in steel construction – with one of the biggest risks from unsecured bolted joints, subjected to any kind of dynamic loads, being the loss of preload and loosening, which could lead to several negative consequences, such as production downtime and unintended movements. That is why Nord-Lock believes that the purposeful and sensible choice of one or more measures is one of the many responsible decisions of the designing engineer.

Challenges: Preload, slackening and self-loosening

Nord-Lock underlines that the design principle in steel construction is historically based on a rivet. Having remained unchanged, most steel bolts are designed non-preloaded. This runs contrary to the design principle of a bolt itself, where
you always want to leverage the benefits of proper clamping and pretensioning.

Loss of preload in bolted joints can occur due to slackening or self-loosening.

Solutions: Nord-Lock washers and European standards

In general, overcoming slackening involves implementing design principles, but self-loosening can be solved with Nord-Lock washers. The washers are validated as an effective securing element for bolted joints by European Technical Assessments (ETAs).  

Will Lowry Content Director t: +44 (0) 1727 743 888

Will joined Fastener + Fixing Magazine in 2007 and over the last 12 years has experienced every facet of the fastener sector – interviewing key figures within the industry and visiting leading companies and exhibitions around the globe. Will manages the content strategy across all platforms and is the guardian for the high editorial standards that the brand is renowned.